1. Field of the Art
The present invention relates to electronic fuel injection systems, and more particularly, to an improved electronic fuel injection control system for multi-cylinder fuel injection control in large combustion engines.
2. Discussion of the Related Art
As is well known, electronic fuel injection systems operate by controlling a solenoid to open and close a fuel injection valve, where the fuel injection valve is electromagnetically coupled to the solenoid. When the valve is opened, fuel is injected into a cylinder bore. In its simplest form, such a fuel injection valve may be opened by applying a constant voltage across the terminals of the solenoid, thereby energizing the solenoid and opening the valve. However, and as described in copending U.S. patent application S/N 08/083,613 (the '613 application)--filed Jun. 28, 1993, now U.S. Pat. No. 5,398,724 issued Mar. 21, 1995, entitled High Speed Electrically Actuated Gaseous Fuel Admission Valve, assigned to the assignee of the present invention, and hereby incorporated by reference--in very large internal combustion engines it is desired to provide balanced operation of the solenoids for each cylinder. This balanced operation is provided in part by circuitry adapted to control the current flow through the solenoid, and in part through a central controller which generates electronic control signals for operating the control circuitry.
More specifically, the control circuitry includes separate driver and control circuits disposed on opposite sides of the solenoids. The driver circuit delivers a current-limited energizing voltage of approximately one hundred volts to one terminal (hereinafter "drive terminal") of each solenoid. The control circuit is electrically connected to the other terminal (hereinafter "control terminal") of each solenoid, and operates to complete the current path through the solenoid by controllably and intermittently grounding the control terminal so as to effect a predetermined current flow through the solenoid. Both the driver and control circuits have an input signal generated by a central or master controller, which serves to turn on and off the operation of the respective driver and control circuits.
Typically, such prior art systems have a dedicated driver and control circuit associated with each solenoid. The driver and control circuits and, therefore, the solenoids are independently operated and controlled by the central controller. Some prior art systems are known, however, to have only a single driver circuit which has its output electrically connected to the drive terminal of each solenoid. Independent control circuits, however, remain dedicated to each solenoid in order to maintain independent control over the individual solenoids.
Regardless of whether the system utilizes a single or multiple driver circuit, the system operates as follows: Control signals generated by the central controller are input to the appropriate driver and control circuits to energize a given solenoid and, thus, open the corresponding fuel injection valve. Precise and repeated operation of the fuel injection valve is achieved by effecting tight control over the current through the solenoid. In this regard, it is desired to open the valve quickly by initially applying a relatively large magnitude current through the solenoid. Then, the current is reduced to a lower magnitude holding current, sufficient to retain the valve in its fully open position. Finally, rapid closure of the fuel injection valve is achieved by breaking the current path through the solenoid and quickly dissipating the energy stored therein.
The precision control of the current through the solenoid and, thus, the operation of the fuel injection valve described above is achieved by the control circuit being configured to intermittently ground the control terminal so as to pulse-width modulate the voltage applied across the terminals of the solenoid. Since the control circuitry utilized to effect this current control is duplicated for each solenoid, a more balanced operation among the cylinders, and thus improved engine operation, is achieved.
While such systems do provide effective control of large multi-cylinder internal combustion engines, further improvements are desired. In this regard, cost is always a significant factor in any system design. It is observed that the cost associated with the prior art systems is inflated in some measure due to the replication of the driver and control circuitry for each cylinder. This replication in circuitry is particularly noteworthy since, due to the sequential firing of the cylinders, typically only one solenoid will be energized at any given time. Accordingly, only one driver and one control circuit will be active at any given time.
Additional shortcomings of the prior art systems are reliability and power consumption. As the number of system components is increased, the overall system reliability is decreased, due to the normal lifetime and expected failure of the individual components. Also, the excessive circuitry increases the power demands of the system.
The problems highlighted above are further compounded as the number of engine cylinders is increased. To be sure, many large stationary internal combustion engines, have sixteen to twenty cylinders. In such systems, the expense and other shortcomings of the prior art become particularly acute.